From: David Edmondson <dme@dme.org>
To: Igor Mammedov <imammedo@redhat.com>,
Eduardo Habkost <ehabkost@redhat.com>
Cc: Laurent Vivier <lvivier@redhat.com>,
Thomas Huth <thuth@redhat.com>,
"Michael S. Tsirkin" <mst@redhat.com>,
Richard Henderson <richard.henderson@linaro.org>,
qemu-devel@nongnu.org, Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [RFC PATCH 1/2] hw/i386: -cpu model,-feature,+feature should enable feature
Date: Wed, 20 Jan 2021 10:08:11 +0000 [thread overview]
Message-ID: <cun4kjb9b04.fsf@dme.org> (raw)
In-Reply-To: <20210120105924.3ffd1723@redhat.com>
On Wednesday, 2021-01-20 at 10:59:24 +01, Igor Mammedov wrote:
> On Tue, 19 Jan 2021 11:30:52 -0500
> Eduardo Habkost <ehabkost@redhat.com> wrote:
>
>> On Tue, Jan 19, 2021 at 04:27:56PM +0000, David Edmondson wrote:
>> > On Tuesday, 2021-01-19 at 10:20:56 -05, Eduardo Habkost wrote:
>> >
>> > > Hi,
>> > >
>> > > Thanks for the patch. Getting rid of special -feature/+feature
>> > > behavior was in our TODO list for a long time.
>> > >
>> > > On Tue, Jan 19, 2021 at 02:22:06PM +0000, David Edmondson wrote:
>> > >> "Minus" features are applied after "plus" features, so ensure that a
>> > >> later "plus" feature causes an earlier "minus" feature to be removed.
>> > >>
>> > >> This has no effect on the existing "-feature,feature=on" backward
>> > >> compatibility code (which warns and turns the feature off).
>> > >
>> > > If we are changing behavior, why not change behavior of
>> > > "-feature,feature=on" at the same time? This would allow us to
>> > > get rid of plus_features/minus_features completely and just make
>> > > +feature/-feature synonyms to feature=on/feature=off.
>> >
>> > Okay, I'll do that.
>> >
>> > Given that there have been warnings associated with
>> > "-feature,feature=on" for a while, changing that behaviour seems
>> > acceptable.
>> >
>> > Would the same be true for changing "-feature,+feature"? (i.e. what this
>> > patch does) Really: can this just be changed, or does there have to be
>> > some period where the behaviour stays the same with a warning?
>>
>> I actually expected warnings to be triggered when using
>> "-feature,+feature" as well. If we were not generating warnings
>> for that case, it will need more careful evaluation, just to be
>> sure it's safe. Igor, do you remember the details here?
> As part of preparation to define/create machines via QMP,
> I plan to post patch(s) to deprecate +-features in 6.0
> (including special casing for -feat behavior (affects x86/sparc only))
> and drop support for +-feat in 2 releases.
> So we should end up with canonical property behavior only like all other
> CPUs and devices.
In that case I will abandon this change and focus on getting my upstack
consumer to switch away from using +-.
Thanks.
dme.
--
Sometimes these eyes, forget the face they're peering from.
next prev parent reply other threads:[~2021-01-20 10:10 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-19 14:22 [RFC PATCH 0/2] x86 CPU feature +/- fiddling and +kvm-no-defaults David Edmondson
2021-01-19 14:22 ` [RFC PATCH 1/2] hw/i386: -cpu model, -feature, +feature should enable feature David Edmondson
2021-01-19 15:20 ` [RFC PATCH 1/2] hw/i386: -cpu model,-feature,+feature " Eduardo Habkost
2021-01-19 16:27 ` [External] : " David Edmondson
2021-01-19 16:30 ` Eduardo Habkost
2021-01-20 9:59 ` Igor Mammedov
2021-01-20 10:08 ` David Edmondson [this message]
2021-01-20 10:08 ` Daniel P. Berrangé
2021-01-20 10:17 ` David Edmondson
2021-01-20 16:18 ` Eduardo Habkost
2021-01-20 19:21 ` Igor Mammedov
2021-01-20 20:12 ` [PATCH] docs/system: Deprecate `-cpu ...,+feature,-feature` syntax Eduardo Habkost
2021-01-20 20:19 ` [PATCH] docs/system: Deprecate `-cpu ..., +feature, -feature` syntax David Edmondson
2021-01-21 9:39 ` [PATCH] docs/system: Deprecate `-cpu ...,+feature,-feature` syntax Daniel P. Berrangé
2021-01-27 0:14 ` John Snow
2021-01-21 10:25 ` Igor Mammedov
2021-01-19 14:22 ` [RFC PATCH 2/2] target/i386: Add "-cpu +kvm-no-defaults" David Edmondson
2021-01-19 16:28 ` [RFC PATCH 0/2] x86 CPU feature +/- fiddling and +kvm-no-defaults Daniel P. Berrangé
2021-01-19 16:35 ` Eduardo Habkost
2021-01-19 16:41 ` Daniel P. Berrangé
2021-01-20 10:01 ` Igor Mammedov
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